17. Submarines conducted pre-invasion surveys and reconnaissance
Their covert nature made submarines ideal for scouting the various islands and atolls considered targets as the US Navy drove across the central Pacific. Submarines both landed parties of scouts and surveyors and explored and photographed Japanese defenses and installations. By 1944 submarines conducted coastal surveys of the home islands of Japan. The missions provided data needed by the planners of the invasion of Japan, and the Army Air Force for bombing targets. Submarines scoured the facilities in the Aleutians in 1942 and 1943, preparatory to the American assault to retake Attu. Submarines studied the defenses of Tarawa, Kwajalein, Guam, Saipan, Iwo Jima, Okinawa, and virtually every island invaded in the Pacific.
With rare exceptions, these missions were conducted with the submarines still under their primary orders, which were simply “sink enemy ships” By the end of 1943, Admiral Lockwood had the aggressive commanders he desired in charge of nearly all of the vessels under his command. Submarine bases and tender facilities pushed forward, to Midway Island, eventually to Apra Harbor in Guam, after that island’s recapture. With far shorter voyages to their patrol areas, submarines could remain on the hunt for enemy ships for longer periods. One hunting area remained closed to them, despite the knowledge it was crowded with Japanese shipping. Since the loss of USS Wahoo in October 1943, Lockwood barred his boats from entering the Sea of Japan.